This application is based on Application No. 2000-315185, filed in Japan on Oct. 16, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
This invention relates to a switching apparatus which employs the interaction of magnetic fields produced by opposing coils having currents flowing through them to generate a drive force which can open and close electrodes to make or interrupt a circuit.
2. Description of the Related Art
FIGS. 24A and 24B are diagrams showing the structure of a switching apparatus utilizing electromagnetic repulsive force. The illustrated switching apparatus includes a switch portion 3 which carries out opening and closing of an electric circuit, a movable shaft 5 which transmits a drive force which opens and closes the switch portion 3, an operating mechanism 9 which exerts a drive force on the movable shaft 5 to open and close the switch portion 3, and a control circuit 30 which controls the operating mechanism 9.
The switch portion 3 includes a fixed electrode 1 which is secured to a stationary support plate 16 and a movable electrode 2 which is disposed opposite the fixed electrode 1. In order to obtain good arc extinguishing properties for the switch portion 3, the electrodes 1 and 2 are housed in an evacuated chamber 4. A first terminal 14 is connected to the fixed electrode 1 and a second terminal 15 is connected to the movable electrode 2. The switch portion 3 can be connected to an external electric circuit through these terminals 14 and 15.
The movable shaft 5 includes a live portion 6 connected to the movable electrode 2 and a non-live portion 7 connected to the operating mechanism 9. The live portion 6 and the non-live portion 7 are connected to each other by an electrically insulating rod 8 which prevents current from flowing from the switch portion 3 to the operating mechanism 9.
The operating mechanism 9 includes a contact opening fixed coil 11 which is secured to a stationary support plate 17, a contact closing coil 12 which is secured to another stationary support plate 18, a movable coil 10 which is secured to movable shaft 5 and which is disposed between contact opening fixed coil 11 and contact closing fixed coil 12, and a bidirectional biasing spring 13 which is secured to a spring support plate 19 and to non-live portion 7 of the movable shaft 5. The movable shaft 5 can freely pass through support plate 17 and support plate 18, so the movable coil 10 can freely reciprocate between contacting opening fixed coil 11 and contact closing fixed coil 12. The biasing spring 19 is a non-linear spring which exerts a biasing force which changes in direction depending on the position of the movable shaft 5. Namely, when the movable shaft 5 is in the raised position shown in FIG. 24A, the biasing spring 19 exerts an upwards biasing force on the movable shaft 5 to maintain the contacts of the switch portion 3 in a closed state, and when the movable shaft 5 is in the lowered position shown in FIG. 24B, the biasing spring 19 exerts a downwards biasing force on the movable shaft 5 to maintain the contacts of the switch portion 3 in an open state. A biasing spring of this type is disclosed in Japanese Patent Laid-Open No. 2000-048683, laid-open on Feb. 18, 2000, for example.
FIG. 25 is a circuit diagram of one example of the control circuit 30 for the operating mechanism 9. The control circuit 30 includes a contact opening electric power storage device 31a, such as a capacitor, which stores electrical energy for contact opening, a contact closing electric power storage device 31b, such as another capacitor, which stores electrical energy for contact closing, a contact opening switch 32a comprising a semiconductor element, such as a thyristor, for contact opening, a contact closing switch 32b also comprising a semiconductor element, such as a thyristor, for contact closing, an opening diode 33a connected between contact opening fixed coil 11 and movable coil 10, a contact closing diode 33b connected between contact closing fixed coil 12 and movable coil 10, and diodes D1, D2, D3, which are connected in parallel with contact opening fixed coil 11, movable coil 10, and contact closing fixed coil 12, respectively, and which release the electromagnetic energy which is stored in the corresponding coils. During use of the switching apparatus, electric power is supplied to the electric power storage devices 31a and 31b by a DC power supply 34 connected as shown in the figure.
Next, contact opening operation will be explained. When the switching apparatus is in the closed contact state shown in FIG. 24A, if the contact opening switch 32a of FIG. 25 is turned on, a pulse current flows from the contact opening electric power storage device 31a through the contact opening switch 32a to the contact opening fixed coil 11, and a magnetic field is generated. At the same time, a pulse current flows through the contact opening diode 33a to the movable coil 10, and a magnetic field having the opposite direction from the magnetic field generated in the contact opening fixed coil 11 is generated in the movable coil 10. Due to the interaction of the magnetic fields generated in the two coils 10 and 11, a repelling force is generated, the movable coil 10 is pushed downwards in the figure, the movable shaft 5 which is secured to the movable coil 10 is also pushed downwards, and the contacts of the switch portion 3 are opened.
When the pulse current is no longer supplied, the electromagnetic energy which is stored in the contact opening fixed coil 11 and the movable coil 10 passes through diodes D1 and D2, respectively, and gradually decreases by circulating in coils 11 and 10.
At this time, due to diode 33b, the pulse current does not flow into the contact opening fixed coil 12, so a magnetic field is not generated by this coil 12.
Next, contact closing operation will be explained. When the switching apparatus is in the open contact state shown in FIG. 24B, if contact closing switch 32b of FIG. 25 is turned on, a pulse current flows from contact closing electric power storage device 31b through contact closing switch 32b to contact closing fixed coil 12, and a magnetic field is generated by this coil 12. At the same time, a pulse current also flows through contact closing diode 33b to movable coil 10, and a magnetic field having the opposite direction from the magnetic field generated by contact closing fixed coil 12 is generated by movable coil 10. Due to the interaction of the magnetic fields generated between these two coils, a repulsive force is generated, the movable coil 10 is pushed upwards in the figure, the movable shaft 5 secured to the movable coil 10 in FIG. 24B is also pushed upwards, and the contacts of switch portion 3 are closed.
Due to an action similar to the contact opening operation, when a pulse current is no longer supplied, the electromagnetic energy stored in the contact closing fixed coil 12 and movable coil 10 passes through diodes D3 and D2, respectively, and circulates in coil 11 and 10, respectively, and gradually decreases.
The switching device of FIGS. 24A and 24B carries out switching by electromagnetic repulsive action which repulses coils from each other, so the speed of operation is fast. However, due to the impact between coils caused by this high speed operation, a large impact force is generated by the movable coil and the fixed coils, and this device has the problem that the securing portions of the coils may be damaged.
In addition, in the device of FIGS. 24A and 24B, a single movable coil is used to perform both contact opening and contact closing, and there is a limit on the speed of operation when a driving force is provided only by an electromagnetic repulsive force, so the illustrated device has the problems that it is difficult for it to cope with demands for increased speed and control modifications.
The present invention was made in order to solve problems like those described above. An object of the present invention is to provide a switching apparatus which prevents damage to coils, which can increase the speed and responsiveness of operation, and which has good stability and highly reliable control.
According to one form of the present invention, a switching apparatus includes a switch portion having a fixed electrode and a movable electrode which is movable with respect to the fixed electrode between an open and a closed position to open and close the switch portion. A movable shaft extends from the movable electrode and is movable by an operating mechanism having a pair of fixed coils and a pair of movable coils. The movable coils are operatively connected to the movable shaft for translating the movable shaft in its axial direction. One of the pairs of coils is disposed between the other pair of coils. A controller controls a supply of current to the coils of the operating mechanism.
The operating mechanism may include a support plate connected to the movable shaft, with the movable coils being disposed back to back on opposite sides of the support plate and being supported by the support plate between the fixed coils.
The operating mechanism may also include an outer frame connected to the movable shaft and a support plate supported by the outer frame, with the movable coils being disposed back to back on opposite sides of the support plate and being supported by the support plate between the fixed coils.
In another form of the present invention, the operating mechanism may include a support plate, with the fixed coils being disposed back to back on opposite sides of the support plate and being supported by the support plate between the movable coils, and with the movable coils being connected to the movable shaft.
The coils of the operating mechanism may comprise a first set of coils comprising one of the fixed coils and one of the movable coils, and a second set of coils comprising the other of the fixed coils and the other of the movable coils. In one form of the present invention, the controller supplies current to one of the sets of coils but not to the other set of coils to repel the two coils of the one set from each other to open the switch portion and supplies current to the other set of coils but not to the one set of coils to repel the two coils of the other set from each other to close the switch portion.
In another form of the present invention, during opening or closing of the switch portion, the controller supplies current to one of the sets of coils to repel the two coils of the one set from each other and simultaneously supplies current to the other set of coils to attract the two coils of the other set to each other.
In yet another form of the present invention, during opening or closing of the switch portion, the controller supplies current to one of the sets of coils to repel the two coils of the one set from each other and subsequently supplies current to the other set of coils to attract the two coils of the other set to each other.
In still another form of the present invention, the controller supplies current to a set of coils prior to contact between the two coils of the set of coils to repel the two coils from each other and generate a braking force.